Renewable energy sources like wind, sun, and hydro are seen as a reliable alternative to the traditional energy sources such as oil, natural gas, or coal. Distributed power generation systems (DPGSs) based on renewable energy sources experience a large development worldwide, with Germany, Denmark, Japan, and USA as leaders in the development in this field. Due to the increasing number of DPGSs connected to the utility network, new and stricter standards in respect to power quality, safe running, and islanding protection are issued. As a consequence, the control of distributed generation systems should be improved to meet the requirements for grid interconnection. This paper gives an overview of the structures for the DPGS based on fuel cell, photovoltaic, and wind turbines. In addition, control structures of the grid-side converter are presented, and the possibility of compensation for low-order harmonics is also discussed. Moreover, control strategies when running on grid faults are treated. This paper ends up with an overview of synchronization methods and a discussion about their importance in the control

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Overview of Control and Grid Synchronization for Distributed Power Generation Systems

The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power-electronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the power-system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. A review of the appropriate storage-system technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented

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Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey

This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.

A review of single-phase grid-connected inverters for photovoltaic modules

This book, written by two major figures in adaptive control, provides a wealth of material for researchers, practitioners, and students. While some researchers in adaptive control may note the absence of a particular topic, the book‘s scope represents a high-gain instrument. It can be used by designers of control systems to enhance their work through the information on many new theoretical developments, and can be used by mathematical control theory specialists to adapt their research to practical needs. The book is strongly recommended to anyone interested in adaptive control.

Adaptive Control

Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

This paper presents a novel approach to power converter design and optimization, where the optimal component characteristics for a DC-DC converter architecture are selected given a specified objective function and various design constraints. Extensive amounts of component data available on commercial distributor sites are used to train supervised regression Machine Learning (ML) models used throughout the optimization algorithm. Using ML-based techniques allows the data-based optimization task to become tractable over a large design space. The developed tool can be used to compare performance measures across converter topologies or component technologies and to predict performance contributions of indi-vidual components. As an example, optimized designs of 48-to-12 V, 5 A buck converters based on GaN and Si MOSFETs are compared in terms of losses, size and cost.

An Approach to DC-DC Converter Optimization using Machine Learning-based Component Models

In this paper we present a custom IC design and experimental results for a hardware efficient 16 phase digital modulator implemented in a 0.35 mum process. The hardware efficient realization is achieved by time sharing the high resolution portion of the modulator hardware and a simple solution to track phase rotation. The modulator is designed for a duty cycle update rate at 16 times the single phase switching frequency to enable wide bandwidth multiphase converter operation. Two versions of the time shared high resolution portion of the IC are realized, including counter based and self tuning delay line based designs. Design details and experimental results are given to evaluate the two options and demonstrate performance of the IC

Implementation of a 16 Phase Digital Modulator in a 0.35 /spl mu/m Process

A second order sliding mode (SOSM) buck controller with near-optimal transient response characteristics has previously been described. This paper shows that the performance of this controller can degrade very significantly in the presence of output capacitor equivalent series resistance and inductance (ESR and ESL, respectively). The reasons for this degradation are developed here, and include the introduction of trajectory discontinuities by the ESR/ESL. This paper then presents a modified SOSM buck controller specifically designed to work well in the presence of ESR/ESL. Simulation results demonstrate the superior performance of the new design in a practical point-of-load buck converter.

Second order sliding mode control of a buck converter with output capacitor ESR and ESL

Predictions of the reduced-order ladder model and the full-order extended cantilever model are compared with the measured behavior of an experimental multiple-output flyback converter. The flyback transformer geometry was chosen to closely follow the idealizing assumptions that lead to the ladder approximation, including use of a pot core with full-width copper foil windings. In spite of this, the ladder model fails to predict the observed waveforms and the mode of operation. The full-order extended cantilever model does indeed correctly predict the operating mode and the observed waveforms. Model parameters are measured using a network analyzer. Conditions on the validity of these measurements are derived using Middlebrook's extra element theorem.

A comparison of the ladder and full-order magnetic models

Cascaded inverters are widely applied in applications where elevated ac voltages are required while using semiconductor devices with lower voltage ratings. Here, we focus on structures that require localized power transfer between low-voltage sources/loads dispersed across inverter dc links and the inverter ac-sides are series-connected across a three-phase medium-voltage ac grid. To date, decentralized controllers that allow for bi-directional power transfer in such systems are limited. To fill this gap, we propose a virtual oscillator controller which modulates the power processed by each inverter in a purely decentralized manner. The proposed controller uses only locally measured current, provides communication-free synchronization of the inverter modules, and enables control of power transfer in both directions. Moreover, it is implemented purely in time domain as opposed to phasor-domain based droop controllers. Stability is analyzed and a design procedure for the oscillator parameters is provided alongside relevant simulation and experimental results for a system of five series-connected inverters.

Dragan Maksimovic

Papers

An Approach to DC-DC Converter Optimization using Machine Learning-based Component Models

Implementation of a 16 Phase Digital Modulator in a 0.35 /spl mu/m Process

Second order sliding mode control of a buck converter with output capacitor ESR and ESL

A comparison of the ladder and full-order magnetic models

Grid-connected Self-synchronizing Cascaded H-Bridge Inverters with Autonomous Power Sharing